I have two walbro 340's running at battery voltage (8AWG wire, 40A fuse, 40A relay triggered by AEM EMS). They definitely sing, esp when standing outside the car over the HKS Super Dragger (PT63, 3", no cats). Inside the car I can just barely make them out at idle when over 1/4 tank and they are noticeably audible when below 1/4 tank. I cannot hear them at all above idle or at any vehicle speed. I'm very sensitive to noise and prefer my car to be quiet until opened up. Loud and/or constant frequency tones bother me. Unless you're as bad as me about sound, it shouldn't be a problem.